This project is proposed as a means of obtaining information applicable to developing a detailed explanation of the molecular events involved in photoreceptor function. Of particular interest is the transduction step in which a photon is absorbed by rhodopsin resulting in a hyperpolarization of the rod outer segment plasma membrane. This will be accomplished by studying light stimulated ion release from bovine retinal rod outer segment disc membranes. Work with disc membranes will be supplemented by comparative measurements in reconstituted systems formed from purified rhodopsin and phospholipids. In addition, associated enzyme functions will be studied in the disc membrane and in reconstituted systems. By this approach, the dependence of various disc properties can be studied as a function of phospholipid composition. BIBLIOGRAPHIC REFERENCES: Microviscosity of the Hydrocarbon Region of the Bovine Retinal Rod Outer Segment Disc Membrane Determined by Fluorescence Probe Measurements. G.W. Stubbs, B.J. Litman, and Y. Barehnolz, Biophys. J. (Society Abstracts of the 20th Annual Meeting) 16, 107A (1976). Dependence of Size Distributions of Phospholipid Vesicles on Lipid Composition, J.H. Goll, Y. Barenholz, B.J. Litman and T.E. Thompson, Biophysical J. (Society Abstracts of the 20th Annual Meeting) 16, 196a (1976).